The present invention relates to a spectrally sensitized silver halide photographic material. More particularly, the present invention relates to a silver halide photographic material having high spectral sensitivity and improved storage stability.
Various compounds have conventionally been used in combination to provide silver halide photographic materials with improved spectral sensitivity in the green range. Exemplary combinations include the use of two kinds of oxacarbocyanine compounds as described in JP-B-44-32753 (the term "JP-B"- as used herein means an "examined Japanese patent publication") and JP-A-52-23931 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), oxacarbocyanine combined with benzimidazolocarbocyanine as described in JP-A-59-16646, and oxacarbocyanine in combination with oxathiacarbocyanine as described in JP-A-60-42750 and JP-A-63-167348. Two kinds of thiacarbocyanine compounds have also been used to provide improved spectral sensitivity in the red range as described in JP-B-43-4933, JP-B-47-8741 and JP-B-51-5781.
However, these compounds often cause desensitization in multi-layered silver halide photographic materials. It is not completely clear why this problem which seldom occurs in single layered structures should take place in multi-layered structures but it is speculated that the multi-layered structure would cause desorption of adsorbed dyes or rearrangement of the same.
With a view to solving this problem, various methods have been tried to enhance the adsorption of dyes such as by changing the halide composition of silver halide emulsions or the crystal habit of silver halide grains or by adding halogens. However, the effectiveness of these methods has been limited by the fact that the change in the conditions for the formation of silver halide crystals inevitably results in variations in the ripening conditions and other factors, thus causing adverse effects in photographic performance characteristics such as a balance between one emulsion layer and the other emulsion layers or the keeping quality of photographic materials.
It has therefore been desired to develop a method of spectrally sensitizing silver halide photographic materials that is free from the defects described above and which is capable of providing them with enhanced sensitivity to light.